Explosive gel composition cross-linked with a hydroxy compound



United States Patent 3,344,004 EXPLOSIVE GEL COMPOSITION CROSS-LINKED WITH A HYDROXY COMPOUND Armand J. Desmarais, Wilmington, DeL, assignor to Hercules Incorporated, a corporation of Delaware N Drawing. Filed Feb. 11, 1966, Ser. No. 526,698 3 Claims. (Ci. 1420) The present invention relates to gelled explosives compositions and process, and more particularly to gelled ammonium nitrate explosive compositions containing certain cross-linked anionic polymers as gelling agent and process of preparing said compositions.

Explosive compositions in the form of slurries are widely used commercially, e.=g., in blasting operations where the slurry is loaded directly into the borehole and detonated. These slurries, which are practically always aqueous slurries, contain various suspended solid ingredients. Typical ingredients of such conventional slurries include water, an inorganic oxidizer salt such as, e.g., ammonium nitrate or sodium nitrate or a mixture of the two, and an explosive sensitizer such as, e.g., smokeless powder, trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RD'X), pentaerythritol tetranitrate (PETN), and mixtures thereof. In order to give the desired performance, the ingredients must remain stably and uniformly suspended in the slurry until the explosive composition is used.

Heretofore various materials have been used in an effort to maintain the ingredients stably and uniformly suspended in the slurry. Although most of the prior art dispersion stabilizers fall in the category of mere thickeners or viscosifiers, instead of gelling agents, they are too often erroneously referred to in this art as gelling agents. The consistency of such prior art thickened explosive compositions is such that they are in the form of a thickened but noncohesive, easily pourable slurry whereas the consistency of explosive compositions of the present invention is such that they are in the form of an elastic, cohesive, three-dimensional, nonpourable :gel. An explosive composition of the latter consistency is desirable not only in order to maintain the ingredients suspended therein but also for the equally important reason of maintaining the explosive composition as an intact, cohesive mass in a readily detonatable condition over a prolonged period of time regardless of underground water which is often present in the borehole.

In accordance with the present invention it has been found that an explosive composition is provided which has the desired consistency of an elastic, cohesive threedimensional, nonpourable gel by carrying out the process which comprises slurrying in water at a pH of about 3-7 a (a) an inorganic oxidizer salt (b) an explosive sensitizer (c) a gelling agent comprising a water soluble anionic polymer which contains carboxylate groups selected from the group consisting of (l) cellulose ethers (2) polymers of acrylic acid, substituted acrylic acid and their alkali metal salts (3) copolymers of acrylamide and the materials listed in (2) above and (4) mixtures containing polymers from at least two of (1), (2) and (3) above The following examples illustrate particular ways in which the present invention may be carried out, but these examples are not intended to limit the invention beyond the scope of the appended claims. In these examples and elsewhere herein, unless otherwise indicated, parts and percent are by weight.

Examples 112-Ta ble I In Examples 1-8 the ammonium nitrate, sodium nitrate, and smokeless powder were slurried in water. One-half of the total amount of gelling agent employed was stirred into this slurry for 30 minutes. Then the crosslinking agent, remaining gelling agent, acid and sugar were stirred into the slurry for 5 minutes and the final slurry allowed to stand. In Examples 9-11 the ammonium nitrate, sodium nitrate, and smokeless powder were slurried in water as in Examples 1-8. A dry blend of the gelling agent, cross-linking agent, acid and sugar was stirred into the slurry for 5 minutes and the final slurry allowed to stand. In Example 12 the CMC was dissolved in the water and the resulting aqueous solution used in making the slurry according to the procedure of Examples 1-8.

TABLE I Sugar Ammonium Nitrate. Sodium Nitrate Smokeless Powder- Water CMC Acrylamide-Sodium Acrylate Copolymer. Hydroxy Aluminum Acetate-.. Hydroxy Chromium Acetate. Dihydroxy Aluminum Sodium Carbonate Aluminum Hydroxide Ferric Hydroxide Fumarie Acid- In each of the examples of Table 1 hereinbefore there was obtained an elastic, cohesive, three-dimensional, nonpourable gel which performed successfully as a blasting explosive and which maintained these desirable properties for several weeks until used.

The CMC used in the examples had a degree of substitution (D.S.) of approximately 0.7, and it is commerially available as CMC7HXS. It has a Brookfield 1% aqueous solution viscosity of 1000-2800 cps. at 25 C. However, water soluble CMC in general is applicable in the present invention. Although any water soluble CMC (i.e., CMC having a D.S. of about 0.3 up to the 3.0 maximum D.S. possible) is applicable, CMC having a D5. of about 0.65-0.95 is preferred. CMC having a D.S. below this preferred range tends to be less uniform in substitution and therefore does not have quite as good solution properties. CMC having a D5. above this preferred range is somewhat less desirable because it has a lower viscosity and therefore a larger amount of it is required to do a given gelling job in accordance with the present invention.

The amount of CMC applicable is not critical and may vary over a wide range. Although about 0.2%2.5% of CMC by weight of the total explosive mixture gives good explosive gels in accordance with the present invention, about 0.5%1.0% CMC is preferred. As would be expected, the amount of CMC varies somewhat with the viscosity of the CMC employed and the relationship is inverse.

The acrylamide-sodium acrylate copolymer used in the examples was composed of about 90 mole percent acrylamide and 10 mole percent sodium acrylate. The relative proportions of these two are not critical and may vary considerably; provided, however, that all copolymers hereof should contain at least about 0.1 mole percent, preferably about -25 mole percent, and may contain up to about 50 or more mole percent of the portion thereof which contains the carboxylate groups. For instance, in the case of acrylamide-sodium acrylate copolymers, the portion which contains the carboxylate groups is (of course) the sodium acrylate units.

The mixtures of gelling agents disclosed as operable herein may be composed of any relative proportions of individual gelling agents and may be added together or separately in any order.

As to amounts and noncriticality thereof, the same applies to other gelling agents (including mixtures) operable herein as disclosed hereinbefore for CMC.

Gelling agents applicable in the present invention, and disclosed hereinbefore more broadly, will now be given in greater detail. The cellulose ethers include the carboxyalkyl cellulose ethers such as, e.g., carboxymethyl cellulose, mixed ethers containing carboxyalkyl substituent groups such as, e.g., carboxyalkyl hydroxyalkyl cellulose ethers including carboxymethyl hydroxyethyl cellulose (CMHEC). In such mixed cellulose ethers the portion thereof which contains the carboxylate groups preferably will be substantial instead of a mere trace. For instance in CMHEC preferably the carboxymethyl D.S. will be at least about 0.4. The hydroxyethyl MS. is not critical and may vary widely, e.g., from a very small value to a very high value such as for instance from about 0.1 or even lower up to about 4 and higher. Methacrylic acid is a substituted acrylic acid of particular interest. A mixture of CMC and acrylamide-sodium acrylate is an example of a mixed polymer which gives excellent results in accordance with the present invention.

Primarily for the sake of simplicity the term gelling agent is used herein with reference to certain polymers defined hereinbefore. However, it is to be understood that the polymers will not give the desired gels unless cross-linked with the cross-linking agents which are defined generally hereinbefore and which will now be given in greater detail. Examples of cross-linking agents of the general formula (HO)MX where M is aluminum, iron or chromium and X is hydroxyl groups are aluminum hydroxide, ferric hydroxide and chromium hydroxide. Typical examples of cross-linking compounds where X is an anion of a fatty acid are hydroxy aluminum (or iron or chromium) acetate. Typical examples of crosslinking compounds where X is an anion of a substituted fatty acid are dihydroxy aluminum (or iron or chromium) amino acetate. Typical examples of cross-linking compounds where X is an anion of an alkali metal carbonate or ammonium carbonate are dihydroxy aluminum sodium (or potassium) carbonate and dihydroxy aluminum ammonium carbonate.

In the preparation of the explosive mixtures of the present invention it is important that the pH of the mixture be about 3-5. Above this pH range the desired gel usually is not formed. Below this pH range syneresis occurs. While somewhat higher pH values (e.g., up to about 7) can be used with such cross-linking agents as for example hydroxy aluminum acetate (see Example 2 hereinbefore), even so it is preferred to operate at a pH no higher than about 5. The means used to give this pH range is not critical according to the present invention. Fumaric acid was employed in the example hereinbefore, but acids in general may be used, either organic or inorganic.

The amount of cross-linking agent is not critical according to the present invention and may vary considerably. Usually the amount of cross-linking agent employed will be about 5%-30%, preferably 15 %-20%, by weight of the gelling agent employed. Cross-linking and gelling according to the present invention occurs simply by mixing the ingredients of the explosive composition.

The ingredients other than gelling agent and cross-linking agent are not per se a part of the present invention. The amounts of such materials as explosive sensitizer, inorganic oxidizer salt and water are not critical in accordance with the present invention but usually are about l5%50%, 45%75% and 10%25%, respectively, by weight of the total explosive mixture. Likewise the amount of sugar, which serves the purpose of an explosive energizer, is not critical and in fact may be omitted entirely.

From the foregoing it will be seen that the critical conditions of the present invention are the gelling agent, cross-linking agent and pH of the explosive composition during mixing (i.e., during cross-linking). For instance such cross-linking agents as those which liberate borate ions (e.g., sodium borate which is commonly known as borax) do not give satisfactory explosive gels in ac cordance with the present invention. The same applies to such materials for example as aluminum alkali metal sulfates, aluminum ammonium sulfate, aluminum chloride, ferric chloride. These unsatisfactory cross-linking agents result either in precipitation of the gelling agent and therefore do not permit a gel to form, or they cause an unsatisfactory gel to form which is brittle and noncohesive.

All of the foregoing examples illustrate employing the present invention in high explosives. The present invention is also applicable in other types of explosives, one of which types is that wherein particulate metals are substituted for the high explosives sensitizer in the foregoing examples. The latter is illustrated in Example 13 hereinafter.

Example 13 A slurry of 50 parts ammonium nitrate, 15 parts sodium nitrate and 18 parts water was heated to F. 0.8 part CMC was stirred into this slurry for 5 minutes. 8 parts aluminum flakes was mixed into the slurry. A dry blend of 0.16 part hydroxy aluminum acetate, 5 parts sugar and 0.1 part fumaric acid was stirred into the slurry for 3 minutes, the slurry cooled to room temperature and lct stand. The pH of the final slurry was 4.9. This gave an elastic, cohesive, three-dimensional, nonpourable gel which performed satisfactorily as an explosive and which maintained these desirable properties for several weeks until used.

From the foregoing examples it will be seen that the present invention contributes novel gelling agent-cross linking agent combinations to the art of gelled explosive compositions. This gelled explosives art is well established and the artisan will readily appreciate that numberous and substantial variations and substitutions regarding the other ingredients may be made within the scope of the present invention.

The acrylamide-sodium acrylate copolymer used in the examples was prepared by copolymerizing acrylamide and sodium acrylate with a free radical initiator.

As many apparent and widely different embodiments of this invention may be made Without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

What I claim and desire to protect by Letters Patent 1. An explosive gel composition comprising (a) an inorganic oxidizer salt (b) an explosive sensitizer (c) water (d) a cross-linked gelling agent comprising a Water soluble anionic polymer which contains carboxylate groups selected from the group consisting of (l) cellulose ethers (2) polymers of acrylic acid, substituted acrylic acid, and their alkali metal salts (3) copolymers of acrylamide and the materials listed in (2) above and (4) mixtures containing polymers from at least two of (1), (2) and (3) above, said gelling agent having been cross-linked with a hydroxy compound having the general formula (HO)MX wherein M is selected from the group consisting of aluminum, iron, and chromium X is selected from the group consisting of hydroxyl groups an anion of a fatty acid an anion of a substituted fatty acid an anion of a compound selected from the group consisting of alkali metal carbonates and ammonium carbonate,

said explosive gel composition having a pH of about 3-7.

2. The explosive gel composition of claim 1 wherein the cross-linked gelling agent is carboxymethylcellulose cross-linked with a compound selected from the group consisting of aluminum hydroxide, ferric hydroxide, hydroxy aluminum acetate, hydroxy chromium acetate, and dihydroxy aluminum sodium carbonate, and wherein the pH of said explosive gel composition is about 3 5.

3. The explosive gel composition of claim 1 wherein the cross-linked gelling agent is acrylamide-sodium acrylate copolymer cross-linked with a compound selected from the group consisting of aluminum hydroxide, ferric hydroxide, hydroxy aluminum acetate, hydroxy chromium acetate, and dihydroxy aluminum sodium carbonate, and wherein the pH of said explosive gel composition is about 3-5.

References Cited UNITED STATES PATENTS 2,826,485 3/1958 Scalera et al 149--52 X 3,072,509 1/1963 Barnhart et al 14947 X 3,097,120 7/1963 Hoffman et al 14960 X 3,097,121 7/1963 Bowkley et al 14960 3,160,538 12/1964 Zaslowsky et al. 14960 X 3,202,556 8/1965 Chrisp 149--57 X 3,214,307 10/1965 Logan et a1 149-18 3,235,425 2/ 1966 Clemens et al 149-53 X 3,242,020 3/1966 Atkins et a1 149-44 X 3,264,151 8/1966 Osborn et a1 14920 X BENJAMIN R. PADGETT, Primary Examiner.

S. J. LECHERT, JR., Assistant Examiner. 

1. AN EXPLOSIVE GEL COMPOSITION COMPRISING (A) AN INORGANIC OXIDIZER SALT (B) AN EXPLOSIVE SENSITIZER (C) WATER (D) A CROSS-LINKED GELLING AGENT COMPRISING A WATER SOLUBLE ANIONIC POLYMER WHICH CONTAINS CARBOXYLATE GROUPS SELECTED FROM THE GROUP CONSISTING OF (1) CELLULOSE ETHERS (2) POLYMERS OF ACRYLIC ACID, SUBSTITUTED ACRYLIC ACID, AND THEIR ALKALI METAL SALTS (3) COPOLYMERS OF ACRYLAMIDE AND THE MATERIALS LISTED IN (2) ABOVE AND (4) MIXTURES CONTAINING POLYMERS FROM AT LEAST TWO OF (1), (2) AND (3) ABOVE, SAID GELLING AGENT HAVING BEEN CROSS-LINKED WITH A HYDROXY COMPOUND HAVING THE GENERAL FORMULA 